docs: def Zhang_Webb(m, x, rhol, mul, P, Pc, D, roughness=0, L=1):
      r'''Calculates two-phase pressure drop with the Zhang-Webb (2001)
      correlation as shown in [1]_ and also given in [2]_.
  
      .. math::
          \phi_{lo}^2 = (1-x)^2 + 2.87x^2\left(\frac{P}{P_c}\right)^{-1}
          + 1.68x^{0.8}(1-x)^{0.25}\left(\frac{P}{P_c}\right)^{-1.64}
  
      Parameters
      ----------
      m : float
          Mass flow rate of fluid, [kg/s]
      x : float
          Quality of fluid, [-]
      rhol : float
          Liquid density, [kg/m^3]
      mul : float
          Viscosity of liquid, [Pa*s]
      P : float
          Pressure of fluid, [Pa]
      Pc : float
          Critical pressure of fluid, [Pa]
      D : float
          Diameter of pipe, [m]
      roughness : float, optional
          Roughness of pipe for use in calculating friction factor, [m]
      L : float, optional
          Length of pipe, [m]
  
      Returns
      -------
      dP : float
          Pressure drop of the two-phase flow, [Pa]
  
      Notes
      -----
      Applicable for 0 < x < 1. Corresponding-states method developed with
      R-134A, R-22 and R-404A in tubes of hydraulic diameters of 2.13 mm,
      6.25 mm, and 3.25 mm. For the author's 119 data points, the mean deviation
      was 11.5%. Recommended for reduced pressures larger than 0.2 and tubes of
      diameter 1-7 mm.
  
      Does not require known properties for the gas phase.
  
      Examples
      --------
      >>> Zhang_Webb(m=0.6, x=0.1, rhol=915., mul=180E-6, P=2E5, Pc=4055000,
      ... D=0.05, roughness=0, L=1)
      712.0999804205621
  
      References
      ----------
      .. [1] Zhang, Ming, and Ralph L. Webb. "Correlation of Two-Phase Friction
         for Refrigerants in Small-Diameter Tubes." Experimental Thermal and
         Fluid Science 25, no. 3-4 (October 2001): 131-39.
         doi:10.1016/S0894-1777(01)00066-8.
      .. [2] Choi, Kwang-Il, A. S. Pamitran, Chun-Young Oh, and Jong-Taek Oh.
         "Two-Phase Pressure Drop of R-410A in Horizontal Smooth Minichannels."
         International Journal of Refrigeration 31, no. 1 (January 2008): 119-29.
         doi:10.1016/j.ijrefrig.2007.06.006.
      '''
      # Liquid-only properties, for calculation of dP_lo
      v_lo = m/rhol/(pi/4*D**2)
      Re_lo = Reynolds(V=v_lo, rho=rhol, mu=mul, D=D)
      fd_lo = friction_factor(Re=Re_lo, eD=roughness/D)
      dP_lo = fd_lo*L/D*(0.5*rhol*v_lo**2)
  
      Pr = P/Pc
      phi_lo2 = (1-x)**2 + 2.87*x**2/Pr + 1.68*x**0.8*(1-x)**0.25*Pr**-1.64
      return dP_lo*phi_lo2